932 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



and to assume that such resemblance, when present, has been inherited. 

 Resemblances are strongest between child and parents, and appear in a dimin- 

 ishing ratio backward along the ancestral line. Galton l has computed that, 

 of the total heritage of the child, each of the two parents contributes one- 

 fourth, each of the four grandparents one-sixteenth, and the remaining one- 

 fourth is handed down by more remote ancestors. The correctness of this 

 estimate has been disputed by Weismanu. The fact must not be overlooked 

 that, in addition to and back of all the particular individual features that are 

 inherited, a host of racial characteristics are transmitted the progeny of a 

 given species belongs to that species ; the human being is the father of the 

 human child, the child of Caucasian parents is a Caucasian, of negro parents 

 a negro. 



Congenital resemblances may be anatomical, physiological, or psychological, 

 and in each of these classes they may be normal or pathological. Anatomical 

 resemblances are the most commonly recognized of all : facial features, stature, 

 color of eyes and of hair, supernumerary digits, excessive hairiness of body, 

 cleft palate, monstrosities, and various defects of the eye, such as those that 

 give rise to hypermetropia, myopia, cataract, color-blindness, and strabismus, 

 are all known examples. Physiological peculiarities that may be transmitted 

 include the tendency to characteristic gestures, locomotion and other muscular 

 movements, longevity or short life, tendency to thinness or obesity, handwriting, 

 voice, haematophilia or tendency to profuse hemorrhage from slight wounds, 

 gout, epilepsy, and asthma. Psychological inheritances comprise habits of 

 mind, talent, artistic and moral qualities, tastes, traits of character, tempera- 

 ment, ambition, insanity and other mental diseases, and tendencies to crime 

 and to suicide. 



Latent Characters ; Reversion. Characters that never appear in the parent 

 may yet be transmitted through him from grandparent to child ; such charac- 

 ters are called latent. Among the most striking latent characters are those con- 

 nected with sex. Darwin 2 says : " In every female all the secondary male 

 characters, and in every male all the secondary female characters, apparently 

 exist in a latent state, ready to be evolved under certain conditions." Thus, a 

 girl may inherit female secondary sexual peculiarities of her paternal grand- 

 mother that are latent in her father, or a boy may inherit from his maternal 

 grandfather characteristics that never show in his mother. An excellent 

 example of such transmission, taken from the herbivora, is the common one 

 of a bull conveying to his female descendants the good milking qualities of 

 his female ancestors. In the human species hydrocele, necessarily a disease of 

 the male, has been known to be inherited from the maternal grandfather, and 

 hence must have been latent in the mother's organism. That in such cases the 

 character is really potential, though latent in the intermediate ancestor, is 

 rendered probable by such well-known facts as the appearance of female cha- 



1 Francis Galton : Natural Inheritance, 1889, p. 134. 



* Charles Darwin: The, Variation of Animals and Plants under Domestication, vol. ii., 2d ed., 

 1892. 



